Distribution and variability of Black Carbon Aerosol and its response to specific Meteorological Occurrences: A case study on the Indian city of Ranchi

Abstract

The black carbon (BC) aerosol is the organic remanence of the incomplete burning of various fuels. The study attempts to analyse the temporal variability of BC over Ranchi, Jharkhand, India using ground based measurements of aethalometer. The diurnal variation reveals two prominent sharp peaks throughout the year, one in the morning hours (0130-0330 UTC) and other in the evening hours (1330-1530 UTC). The results show a marked seasonal variation in BC concentration, with highest value during the pre-monsoon (7.24 µg/m³) and least in the monsoon (2.01 µg/m³) season. The relationship of meteorological variables such as temperature, precipitation, aerosol optical depth (AOD), organic carbon and vegetation represented via Normalized Difference Vegetation Index (NDVI) with BC is also computed using satellite-based measurements. A significant correlation is in the spatial pattern of organic carbon (r = 0.927), AOD (r = 0.86) and temperature (r = 0.748) with BC, whereas precipitation (r = − 0.146) and NDVI (r = − 0.203) shows insignificant correlation with BC. Significantly higher level of BC concentration (11.95 µg/m³) in response to the fog event is observed throughout the day against lower (6.5 µg/m³) BC in winter. The morning peak is increased by 4.71 µg/m³ and delayed by two hours on foggy day than the winter mean. During the thunder squall event, mean BC is reduced to 3.84 µg/m³ from 7.24 µg/m³ in  pre-monsoon. Similar reduction is also observed in mean BC (1.2 µg/m³) in response to a rainy day during monsoon. The variability in BC is key to the changes in AOD that impacts the air quality, energy balance, cloud-precipitation processes, global warming and climate change.